In accordance with a rapid spread of information relevant apparatuses and communication apparatuses such as a personal computer, a video camera and a portable telephone in recent years, the development of a battery to be utilized as a power source thereof has been emphasized. The development of a high-output and high-capacity battery for an electric automobile or a hybrid automobile has been advanced also in the automobile industry. A lithium secondary battery has been presently noticed from the viewpoint of a high energy density among various kinds of batteries.
Liquid electrolyte containing a flammable organic solvent is used for a presently commercialized lithium secondary battery, so that the installation of a safety device for restraining temperature rise during a short circuit and the improvement in structure and material for preventing the short circuit are necessary therefor. On the contrary, a lithium secondary battery solidified by replacing the liquid electrolyte with a solid electrolyte layer is conceived to intend the simplification of the safety device and be excellent in production cost and productivity for the reason that the flammable organic solvent is not used in the battery.
Also, it is known that a secondary battery may be repeatedly charged and discharged but battery performance decreases due to overdischarge. Thus, an ordinary secondary battery is provided with a means of measuring voltage of the battery during discharge to stop the discharge at a predetermined voltage. On the other hand, in Patent Literature 1, a battery module not provided with an overdischarge protective means of preventing a lithium secondary battery from being overdischarged is disclosed; in Patent Literature 2, a conductive device not provided with an overdischarge protective means of preventing a lithium secondary battery from being overdischarged is disclosed.